陳宜恬,梁 宜,2△,杜俊英,2,房軍帆,方劍喬,2
(1.浙江中醫(yī)藥大學(xué)第三臨床醫(yī)學(xué)院針灸神經(jīng)生物學(xué)實(shí)驗(yàn)室,浙江杭州310053;2.浙江中醫(yī)藥大學(xué)附屬第三醫(yī)院,浙江杭州310005)
阿片類藥物常用于緩解疼痛以及疼痛引發(fā)的并發(fā)癥狀,是至今最有效的止痛劑,也是現(xiàn)階段治療癌痛的主要藥物[1]。然而,嗎啡長期使用后產(chǎn)生的成癮和耐受也限制了其臨床效用。μ 阿片受體(Muopioid receptor,MOR)是嗎啡的主要作用受體,是G蛋白偶聯(lián)受體(G-protein-couled receptors,GPCRs)家族中的成員之一。下面就MOR 參與嗎啡耐受的角色進(jìn)行探討。
MOR 有7 個(gè)跨膜螺旋片段,1 個(gè)細(xì)胞外的氨基端區(qū)域和1 個(gè)細(xì)胞內(nèi)的羧基端尾區(qū)[2],目前已發(fā)現(xiàn)MOR 有μ1 型和μ2 型[3]。有研究發(fā)現(xiàn),μ1 型阿片受體在脊髓及脊髓上水平均起鎮(zhèn)痛作用,而μ2 型阿片受體只在脊髓水平發(fā)揮其鎮(zhèn)痛作用[4]。
MOR 在中樞神經(jīng)系統(tǒng)分布廣泛,在三叉神經(jīng)核、楔狀核、丘腦和延腦側(cè)正中部、藍(lán)斑、導(dǎo)水管周圍灰質(zhì)及脊髓背角淺層等處均有分布,其中在中腦和下丘腦表達(dá)最多,而在海馬、紋狀體和腦皮層中表達(dá)量較少,在小腦沒有檢測到MOR mRNA 的存在[4-5];在外周神經(jīng)系統(tǒng)中,MOR 主要分布在背根神經(jīng)節(jié)小型神經(jīng)元細(xì)胞膜表面[6]。MOR 與阿片肽的結(jié)合部位-在腦內(nèi)的分布與痛覺通路平行[7]。此外,研究發(fā)現(xiàn)在大鼠皮膚無髓鞘神經(jīng)纖維和膠質(zhì)細(xì)胞中也有MOR 的表達(dá)[8-9]。
MOR 活化能產(chǎn)生顯著的鎮(zhèn)痛效應(yīng)。研究發(fā)現(xiàn),在正常組織中僅檢測極其少量的MOR,MOR 預(yù)先存在于外周神經(jīng)末梢中,但未被激活,但在炎癥反應(yīng)后數(shù)分鐘至數(shù)小時(shí)即可檢測大量MOR 聚集,MOR 被激活發(fā)揮鎮(zhèn)痛作用[8]。而在MOR 基因敲除的小鼠中,嗎啡的鎮(zhèn)痛作用基本消失,所以嗎啡作為一種阿片受體的強(qiáng)有力的激動(dòng)劑,主要是通過激活MOR 發(fā)揮其鎮(zhèn)痛作用[10]。MOR 的跨膜螺旋片段和嗎啡等MOR 激動(dòng)劑結(jié)合后,會(huì)激活GTP 結(jié)合蛋白(主要是Gi/o 蛋白),通過引起的一系列變化,降低神經(jīng)元的興奮性,從而抑制傷害性信息的傳遞,達(dá)到了鎮(zhèn)痛的作用[11]。
嗎啡耐受發(fā)生后MOR 與G 蛋白的耦聯(lián)發(fā)生了改變,嗎啡仍能通過和MOR 相結(jié)合來引起神經(jīng)元的反應(yīng),但此時(shí)嗎啡激活的G 蛋白已經(jīng)不單是Gi/o,更多的是激活了興奮性的Gs 蛋白,從而激活興奮性信號(hào)通路,產(chǎn)生cAMP,對抗了嗎啡的鎮(zhèn)痛效力[12]。嗎啡耐受的形成過程中通常伴隨著MOR數(shù)量的變化,MOR 數(shù)量變化以胞膜和胞內(nèi)的MOR數(shù)量變化為特征。在體外中慢性給予阿片受體激動(dòng)劑會(huì)引起MOR 的下調(diào),但是體內(nèi)實(shí)驗(yàn)中卻不能得到與體外實(shí)驗(yàn)相似的結(jié)果,不同研究部位MOR 上調(diào)、下調(diào)及數(shù)量無明顯變化均有報(bào)道[13-15],因此,很難評(píng)估MOR 數(shù)量的變化在介導(dǎo)嗎啡耐受中的作用。有人認(rèn)為,MOR 也許是通過與下游信號(hào)傳導(dǎo)系統(tǒng)脫耦聯(lián)的方式以介導(dǎo)嗎啡耐受,而與單獨(dú)受體丟失關(guān)聯(lián)不大[12]。而研究發(fā)現(xiàn),MOR 的失敏及復(fù)敏與嗎啡耐受的關(guān)系最為密切,MOR 失敏能夠促進(jìn)嗎啡耐受的產(chǎn)生,復(fù)敏能夠?qū)箚岱饶褪堋?/p>
長期應(yīng)用阿片類激動(dòng)劑,引起阿片受體磷酸化,與抑制性G 蛋白脫偶聯(lián),阿片受體對阿片肽不再敏感,嗎啡的鎮(zhèn)痛作用減弱,即為受體失敏。阿片受體的失敏是機(jī)體對阿片類藥物產(chǎn)生耐受性的主要分子機(jī)制之一[16]。MOR 磷酸化和失敏至少是通過兩個(gè)截然不同的生化途徑:一是激動(dòng)劑誘導(dǎo)的受體直接磷酸化;二是第二信使激酶中的PKC 誘導(dǎo)的失敏[17]。同時(shí),MOR-DOR 異體二聚物及其他因子也可以促進(jìn)MOR 失敏,繼而促進(jìn)嗎啡耐受的產(chǎn)生。
3.1.1 MOR 磷酸化誘導(dǎo)MOR 失敏
激動(dòng)劑激活MOR 后,在蛋白激酶C(Protein kinase C,PKC)的作用下,誘導(dǎo)MOR 磷酸化和失敏;在G 蛋白偶聯(lián)受體激酶(G-protein-coupled receptor kinases,GRKs)的作用下,誘導(dǎo)MOR 磷酸化,繼而可引起MOR 的失敏和內(nèi)吞。MOR 的羧基端末梢約有20 個(gè)磷酸化位點(diǎn),這些位點(diǎn)的磷酸化對MOR 功能調(diào)節(jié)起著重要的作用。如MOR Ser344、Ser363 和Thr370 位點(diǎn)是PKC 介導(dǎo)的失敏的磷酸化位點(diǎn)[18-20],但是也有研究發(fā)現(xiàn)Ser363 位點(diǎn)的MOR磷酸化在沒有激動(dòng)劑誘導(dǎo)的情況下也能夠發(fā)生[21];MOR Ser394、Ser375 及Ser355/Thr357 是GRK 磷酸化介導(dǎo)的失敏的磷酸化位點(diǎn)[22];Ser266 是鈣離子/鈣調(diào)素依賴性蛋白激酶II(Ca2+/Calmodulin-dependent Protein Kinase,CaMKII)介導(dǎo)的失敏的磷酸化位點(diǎn)[23]。
3.1.2 PKC 途徑介導(dǎo)的MOR 失敏
研究發(fā)現(xiàn)嗎啡主要通過PKC 途徑誘導(dǎo)MOR失敏[24],而PKC 介導(dǎo)的MOR 失敏可能與其誘導(dǎo)MOR 磷酸化,從而降低了MOR 偶聯(lián)G 蛋白的能力有關(guān)[25]。嗎啡耐受后PKC 從胞漿轉(zhuǎn)位至胞膜,轉(zhuǎn)位后的PKC 被激活[26],參與了MOR 的磷酸化和失敏。Bailey[27]等發(fā)現(xiàn),PKC 的激活能夠引起大鼠藍(lán)斑核MOR 的快速失敏,PKC 途徑導(dǎo)致的MOR 失敏主要有直接和間接兩種:PKC 激活能降低MOR 偶聯(lián)G蛋白的能力,直接誘導(dǎo)MOR 磷酸化,此時(shí)的MOR還在細(xì)胞膜上,繼而在arrestin 和網(wǎng)格蛋白參與下,使MOR 功能喪失;同時(shí)PKC 能誘導(dǎo)G 蛋白信號(hào)調(diào)節(jié)蛋白(Regulator of G-protein signaling,RGS)[28-29]和GRK2[30]的磷酸化,從而導(dǎo)致了MOR 的失敏?;蚯贸齈KC 或者應(yīng)用PKC 抑制劑能翻轉(zhuǎn)嗎啡誘導(dǎo)的MOR 脫敏及嗎啡耐受形成[20,24,31]。
而由GRK 通路誘導(dǎo)MOR 的磷酸化可以促進(jìn)MOR 的內(nèi)吞和復(fù)敏,MOR 重新發(fā)揮作用,繼而對抗嗎啡耐受;部分MOR 會(huì)在內(nèi)吞后經(jīng)溶酶體降解[32]。
3.1.3 MOR-DOR 異體二聚物
研究發(fā)現(xiàn),敲除DOR 小鼠不會(huì)出現(xiàn)嗎啡耐受[33],與此同時(shí),也有研究發(fā)現(xiàn)慢性嗎啡處理會(huì)上調(diào)DOR[34],且會(huì)導(dǎo)致MOR 對嗎啡的反應(yīng)性發(fā)生改變[35]。由此,我們可以認(rèn)為,DOR 在嗎啡耐受中也起發(fā)揮著重要的作用。Gomes 等[36]通過研究證明了MOR 和DOR能發(fā)生直接的互相作用,從而形成異體二聚物。DOR 被轉(zhuǎn)運(yùn)至細(xì)胞膜后會(huì)與MOR 進(jìn)行異體寡聚,形成新的信號(hào)轉(zhuǎn)導(dǎo)復(fù)合物[37],促進(jìn)嗎啡耐受的形成。MOR-DOR 異體二聚物是由保持本身結(jié)構(gòu)完整性的MOR 和DOR 單體聚合而成[38],使用嗎啡后,在PKC 的影響下,該異體二聚物會(huì)招募β-arrestin2,繼而引起有絲分裂原激活蛋白激酶及其下游酶的激活和細(xì)胞外信號(hào)調(diào)節(jié)激酶1/2(extracellular signal-regulated kinases 1 and 2,ERK1/2)的磷酸化[39-41],磷酸化后的ERK 被限制在細(xì)胞質(zhì),導(dǎo)致了不同的下游激酶和轉(zhuǎn)錄因子的激活[41],從而促進(jìn)了嗎啡耐受的形成。另外,研究也發(fā)現(xiàn)DOR 被轉(zhuǎn)運(yùn)至胞膜后,會(huì)發(fā)生降解,MOR 也會(huì)受到“牽連”而發(fā)生降解,促進(jìn)嗎啡耐受的形成[12]。
3.1.4 其他因子
另外,鈣離子/鈣調(diào)素依賴性蛋白激酶II(Ca2+/Calmodulin-dependent Protein Kinase,CaMKII)、絲裂元活化蛋白激酶(Mitogen-Activate Protein Kinase,MAPK)介導(dǎo)的MOR 磷酸化在MOR 失敏中也發(fā)揮了重要的作用。在CaMKII 介導(dǎo)的MOR 磷酸化可以引起MOR 失敏,從而促進(jìn)嗎啡耐受的形成,CaMKII 抑制劑能對抗這一作用。MAPK 與MOR 可以相互影響,MOR 活化能夠促進(jìn)MAPK 磷酸化,特別是ERKs[42],而MAKP 通路的激活也可以介導(dǎo)MOR 的失敏,抑制其激活可以促進(jìn)MOR 磷酸化和內(nèi)吞,對抗嗎啡耐受的形成[43]。
失敏后的MOR,脫離胞膜進(jìn)入胞漿,不再發(fā)揮作用,繼而招募β-arrestin 而發(fā)生內(nèi)吞[44],內(nèi)吞后的MOR 脫磷酸化,重新回到胞膜而發(fā)揮作用,這個(gè)過程是MOR 的復(fù)敏。MOR 的復(fù)敏保證了MOR 能夠的功能恢復(fù),MOR 內(nèi)吞是其復(fù)敏的關(guān)鍵第一步。
3.2.1 MOR 內(nèi)吞和復(fù)敏的過程
MOR 內(nèi)吞是一個(gè)快速的過程,在受體和配體結(jié)合后幾分鐘之內(nèi)就會(huì)發(fā)生。新近的研究也表明,MOR 內(nèi)吞可作為一種保護(hù)措施,抑制嗎啡耐受的形成[45-46]。已有研究證實(shí),慢性應(yīng)用嗎啡引起MOR 受體內(nèi)吞和失敏的能力極弱,同時(shí)也降低或不引起內(nèi)吞后MOR 動(dòng)態(tài)循環(huán)復(fù)敏到細(xì)胞膜上[47],從而導(dǎo)致了嗎啡耐受的出現(xiàn)。MOR 失敏后,從胞膜進(jìn)入胞漿,在β-arrestin 和網(wǎng)格蛋白的作用下,形成內(nèi)吞小囊泡[47],完成內(nèi)吞過程。內(nèi)吞后的MOR 有2 種結(jié)局:一部分MOR 被溶酶體內(nèi)的蛋白酶降解[47];另一部分內(nèi)吞的受體發(fā)生脫磷酸化,與激動(dòng)劑分離,重新回到膜上,發(fā)揮正常的功能此為受體的復(fù)蘇[48],即MOR 復(fù)敏。復(fù)敏后的MOR 重新發(fā)揮其作用,所以我們認(rèn)為MOR 的復(fù)敏可以有效對抗嗎啡耐受[49-50]。內(nèi)吞還避免了Gs 信號(hào)通路的過度激活,避免了MOR 的功能發(fā)生改變,從而進(jìn)一步抑制了耐受的發(fā)生[51]。
3.2.2 MOR 內(nèi)吞和嗎啡耐受的關(guān)系
受體的內(nèi)吞被認(rèn)為是受體急性失敏的重要機(jī)制,而受體的磷酸化是內(nèi)吞的重要環(huán)節(jié),而受體復(fù)敏是受體內(nèi)吞后的轉(zhuǎn)歸之一。由GRK 和β-arrestin介導(dǎo)的MOR 磷酸化和失敏可以引起MOR 的內(nèi)吞[52-53],MOR 重新回到胞膜上[47],繼續(xù)發(fā)揮其作用,從而對抗嗎啡耐受。另外,MOR 內(nèi)吞限制了AC 的產(chǎn)生,避免了cAMP 的超活化,從而抑制了嗎啡耐受的產(chǎn)生。
為了更好地說明不同激動(dòng)劑對MOR 內(nèi)吞的影響,現(xiàn)很多研究者都采用了RAVE(Relative Activation Versus Endocytosis)的概念[54]。RAVE 即激動(dòng)劑激活受體的效力和引起受體內(nèi)吞的能力。激活受體能力強(qiáng)同時(shí)又易致內(nèi)吞的為低RAVE 激動(dòng)劑,而激活受體能力強(qiáng)同時(shí)卻不易致內(nèi)吞的為高RAVE 激動(dòng)劑,嗎啡屬于高RAVE 激動(dòng)劑[55]。在離體和在體的實(shí)驗(yàn)研究中,急性或慢性的嗎啡作用可以引起極其少量MOR 的內(nèi)吞[56]。Wang HL[57]發(fā)現(xiàn),在GRK2或β-arrestin 過表達(dá)的神經(jīng)元中,嗎啡能引起MOR的內(nèi)吞。由此我們可以認(rèn)為,GRK 和β-arrestin 的表達(dá)過低可能是嗎啡較難引起MOR 內(nèi)吞的原因。同時(shí),PKC 介導(dǎo)的MOR 磷酸化也能抑制MOR 的內(nèi)吞,而PKC 抑制劑Calphostin C 能引發(fā)MOR 內(nèi)吞[58]。并且研究者發(fā)現(xiàn)可以通過藥理學(xué)方法,如嗎啡聯(lián)合能夠DAMGO [(D-ala2,N-me-phe4,gly5-ol)-enkephalin]或美沙酮,促使能夠促進(jìn)MOR 內(nèi)吞[59]。
嗎啡耐受是疼痛治療過程中的疑難問題,它嚴(yán)重限制了嗎啡類藥物的臨床應(yīng)用;而MOR 作為嗎啡主要激活的阿片受體,在嗎啡鎮(zhèn)痛和耐受中都發(fā)揮了重要作用。長期大量應(yīng)用嗎啡后,MOR 失敏會(huì)加速嗎啡耐受的出現(xiàn),而MOR 的內(nèi)吞作為一種保護(hù)機(jī)制,能夠拮抗嗎啡耐受的形成,并且內(nèi)吞后的MOR 一部分被溶酶體降解,還有一部分可以回到細(xì)胞膜,復(fù)敏以發(fā)揮其作用。通過這個(gè)過程,受體避免了持續(xù)刺激,從而避免了受體發(fā)生長時(shí)間的失敏??上攵?,我們可以從抑制MOR 失敏、加強(qiáng)MOR內(nèi)吞及促進(jìn)MOR 復(fù)敏方面,尋找消除嗎啡耐受的靶點(diǎn)。
[1] Grant M,Ugalde A,Vafiadis P,et al. Exploring the myths of morphine in cancer:views of the general practice population[J]. Support Care Cancer,2014,Epub ahead of print.
[2] Dhawan B N,Cesselin F,Raghubir R,et al. International Union of Pharmacology. XII. Classification of opioid receptors[J]. Pharmacol Rev,1996,48(4):567-592.
[3] Pasternak G W. Insights into mu opioid pharmacology the role of mu opioid receptor subtypes [J]. Life Sci,2001,68(19-20):2213-2219.
[4] Back S K,Lee J,Hong S K,et al. Loss of spinal mu-opioid receptor is associated with mechanical allodynia in a rat model of peripheral neuropathy[J]. Pain,2006,123(1-2):117-126.
[5] Wang C,Shu S Y,Guo Z,et al. Immunohistochemical localization of mu opioid receptor in the marginal division with comparison to patches in the neostriatum of the rat brain[J].J Biomed Sci,2011,18:34.
[6] Hervera A,Negrete R,Leanez S,et al. Peripheral effects of morphine and expression of mu-opioid receptors in the dorsal root ganglia during neuropathic pain:nitric oxide signaling[J]. Mol Pain,2011(7):25.
[7] Arvidsson U,Riedl M,Chakrabarti S,et al. Distribution and targeting of a mu-opioid receptor (MOR1)in brain and spinal cord [J]. The Journal of Neuroscience,1995,15(5):3328-3341.
[8] Patierno S,Anselmi L,Jaramillo I,et al. Morphine induces mu opioid receptor endocytosis in guinea pig enteric neurons following prolonged receptor activation [J]. Gastroenterology,2011,140(2):618-626.
[9] Talbot J N,Roman D L,Clark M J,et al. Differential modulation of mu-opioid receptor signaling to adenylyl cyclase by regulators of G protein signaling proteins 4 or 8 and 7 in permeabilised C6 cells is Galpha subtype dependent [J]. J Neurochem,2010,112(4):1026-1034.
[10] Chen S L,Ma H I,Han J M,et al. Antinociceptive effects of morphine and naloxone in mu-opioid receptor knockout mice transfected with the MORS196A gene [J]. J Biomed Sci,2010,17:28.
[11] Simon E J. Subunit structure and purification of opioid receptors[J]. J Recept Res,1987,7(1-4):105-132.
[12] 劉海青,白波. 阿片類藥物成癮的受體機(jī)制研究進(jìn)展[J].中華行為醫(yī)學(xué)與腦科學(xué)雜志,2011,20(6):571-573.
[13] Kao JH,Gao MJ,Yang PP,et al. The effect of naltrexone on neuropathic pain in mice locally transfected with the mutant mu-opioid receptor gene in spinal cord. [J]. Br J Pharmacol,2014,Epub ahead of print.
[14] Li G,Ma F,Gu Y,et al. Analgesic tolerance of opioid agonists in mutant mu-opioid receptors expressed in sensory neurons following intrathecal plasmid gene delivery [J].Mol Pain,2013,9(63):1-10.
[15] Fernandez-Duenas V,Pol O,Garcia-Nogales P,et al. Tolerance to the antinociceptive and antiexudative effects of morphine in a murine model of peripheral inflammation[J].J Pharmacol Exp Ther,2007,322(1):360-368.
[16] Williams JT,Ingram SL,Henderson G,et al. Regulation of μ-opioid receptors:desensitization,phosphorylation,internalization,and tolerance[J]. Pharmacol Rev,2013,65(1):223-254.
[17] Yu Y,Zhang L,Yin X,et al. Mu opioid receptor phosphorylation,desensitization,and ligand efficacy [J]. J Biol Chem,1997,272(46):28869-28874.
[18] El Kouhen R,Burd A L,Erickson-Herbrandson L J,et al.Phosphorylation of Ser363,Thr370,and Ser375 residues within the carboxyl tail differentially regulates mu-opioid receptor internalization [J]. J Biol Chem,2001,276(16):12774-12780.
[19] Law P,Loh H,Wei L-N. Insights into the receptor transcription and signaling:implications in opioid tolerance and dependence [J]. Neuropharmacology,2004,47:300-311.
[20] Feng B,Li Z,Wang J B. Protein kinase C-mediated phosphorylation of the mu-opioid receptor and its effects on receptor signaling[J]. Mol Pharmacol,2011,79(4):768-775.
[21] Burd A L,El-Kouhen R,Erickson L J,et al. Identification of serine 356 and serine 363 as the amino acids involved in etorphine-induced down-regulation of the mu-opioid receptor[J]. J Biol Chem,1998,273(51):34488-34495.
[22] Wang H L. A cluster of Ser/Thr residues at the C-terminus of mu-opioid receptor is required for G protein-coupled receptor kinase 2-mediated desensitization[J]. Neuropharmacology,2000,39(3):353-363.
[23] Narita M,Matsumura Y,Ozaki S,et al. Role of the calcium/calmodulin-dependent protein kinase ii(CaMKII)in the morphine -induced pharmacological effects in the mouse[J]. Neuroscience,2004,126(2):415-421.
[24] Bailey C P,Oldfield S,Llorente J,et al. Involvement of PKC alpha and G-protein-coupled receptor kinase 2 in agonist-selective desensitization of mu-opioid receptors in mature brain neurons [J]. Br J Pharmacol,2009,158(1):157-164.
[25] Bailey C P,Llorente J,Gabra B H,et al. Role of protein kinase C and mu-opioid receptor(MOPr)desensitization in tolerance to morphine in rat locus coeruleus neurons[J].Eur J Neurosci,2009,29(2):307-318.
[26] Griner E M,Kazanietz M G. Protein kinase C and other diacylglycerol effectors in cancer[J]. Nat Rev Cancer,2007,7(4):281-294.
[27] Bailey C P,Kelly E,Henderson G. Protein kinase C activation enhances morphine-induced rapid desensitization of μ-opioid receptors in mature rat locus ceruleus neurons[J].Molecular pharmacology,2004,66(6):1592-1598.
[28] Garzon J,Rodriguez-Munoz M,Sanchez-Blazquez P. Morphine alters the selective association between mu-opioid receptors and specific RGS proteins in mouse periaqueductal gray matter [J]. Neuropharmacology,2005,48(6):853-868.
[29] Clark M J,Traynor J R. Endogenous regulator of g protein signaling proteins reduce mu-opioid receptor desensitization and down-regulation and adenylyl cyclase tolerance in C6 cells[J]. J Pharmacol Exp Ther,2005,312(2):809-815.
[30] Rodríguez -Mu?oz M,Sánchez -Blázquez P,Vicente -Sánchez A,et al. The mu-opioid receptor and the NMDA receptor associate in PAG neurons:implications in pain control[J]. Neuropsychopharmacology,2012,37(2):338-349.
[31] Huo YP1,Hong YG. Protein kinase C and morphine tolerance [J]. Sheng Li Ke Xue Jin Zhan,2011,42(6):423-426.
[32] Hull L C,Llorente J,Gabra B H,et al. The effect of protein kinase C and G protein-coupled receptor kinase inhibition on tolerance induced by mu-opioid agonists of different efficacy [J]. J Pharmacol Exp Ther,2010,332(3):1127-1135.
[33] Nitsche J F,Schuller A G,King M A,et al. Genetic dissociation of opiate tolerance and physical dependence in delta-opioid receptor-1 and preproenkephalin knock-out mice[J]. J Neurosci,2002,22(24):10906-10913.
[34] Cahill C M,Morinville A,Lee M C,et al. Prolonged morphine treatment targets delta opioid receptors to neuronal plasma membranes and enhances delta-mediated antinociception[J]. J Neurosci,2001,21(19):7598-7607.
[35] Guan J S,Xu Z Z,Gao H,et al. Interaction with vesicle luminal protachykinin regulates surface expression of deltaopioid receptors and opioid analgesia [J]. Cell,2005,122(4):619-631.
[36] Gomes I,Gupta A,F(xiàn)ilipovska J,et al. A role for heterodimerization of mu and delta opiate receptors in enhancing morphine analgesia [J]. Proc Natl Acad Sci U S A.,2004,101(14):5135-5139.
[37] Fan T,Varghese G,Nguyen T,et al. A role for the distal carboxyl tails in generating the novel pharmacology and G protein activation profile of mu and delta opioid receptor hetero-oligomers[J]. J Biol Chem,2005,280(46):38478-38488.
[38] Snook L A,Milligan G,Kieffer B L,et al. Mu-delta opioid receptor functional interaction:Insight using receptor-G protein fusions [J]. J Pharmacol Exp Ther,2006,318(2):683-690.
[39] Belcheva M M,Clark A L,Haas P D,et al. Mu and kappa opioid receptors activate ERK/MAPK via different protein kinase C isoforms and secondary messengers in astrocytes[J]. J Biol Chem,2005,280(30):27662-27669.
[40] Bilecki W,Zapart G,Ligeza A,et al. Regulation of the extracellular signal-regulated kinases following acute and chronic opioid treatment [J]. Cell Mol Life Sci,2005,62(19-20):2369-2375.
[41] Rozenfeld R,Devi L A. Receptor heterodimerization leads to a switch in signaling:beta-arrestin2-mediated ERK activation by mu -delta opioid receptor heterodimers [J].FASEB J,2007,21(10):2455-2465.
[42] Niikura K,Narita M,Butelman E R,et al. Neuropathic and chronic pain stimuli downregulate central mu-opioid and dopaminergic transmission [J]. Trends Pharmacol Sci,2010,31(7):299-305.
[43] 張顏波,孫保亮,袁慧,等. 絲裂原活化的蛋白激酶通路與嗎啡耐受[J]. 基礎(chǔ)醫(yī)學(xué)與臨床,2010(3):325-328.
[44] Dang V C,Chieng B,Azriel Y,et al. Cellular morphine tolerance produced by βarrestin-2-dependent impairment of μ-opioid receptor resensitization[J]. The Journal of Neuroscience,2011,31(19):7122-7130.
[45] He L,Whistler JL. Chronic ethanol consumption in rats produces opioid antinociceptive tolerance through inhibition of mu opioid receptor endocytosis [J]. PLoS One,2011,6(5):e19372.
[46] He L,Kim JA,Whistler JL. Biomarkers of morphine tolerance and dependence are prevented by morphine-induced endocytosis of a mutant mu-opioid receptor [J]. FASEB J,2009,23(12):4327-4334.
[47] Sternini C,Brecha N C,Minnis J,et al. Role of agonist-dependent receptor internalization in the regulation of mu opioid receptors[J]. Neuroscience,2000,98(2):233-241.
[48] von Zastrow M,Svingos A,Haberstock -Debic H,et al.Regulated endocytosis of opioid receptors:cellular mechanisms and proposed roles in physiological adaptation to opiate drugs[J]. Curr Opin Neurobiol,2003,13(3):348-353.
[49] Koch T,Widera A,Bartzsch K,et al. Receptor endocytosis counteracts the development of opioid tolerance [J]. Mol Pharmacol,2005,67(1):280-287.
[50] Whistler J L,Chuang H H,Chu P,et al. Functional dissociation of mu opioid receptor signaling and endocytosis:implications for the biology of opiate tolerance and addiction[J]. Neuron,1999,23(4):737-746.
[51] Shen K F,Crain S M. Cholera toxin-B subunit blocks excitatory effects of opioids on sensory neuron action potentials indicating that GM1 ganglioside may regulate Gslinked opioid receptor functions [J]. Brain Res,1990,531(1-2):1-7.
[52] Li J,Xiang B,Su W,et al. Agonist-induced formation of opioid receptor-G protein-coupled receptor kinase(GRK)-G beta gamma complex on membrane is required for GRK2 function in vivo [J]. J Biol Chem,2003,278(32):30219-30226.
[53] Dang V C,Chieng B,Azriel Y,et al. Cellular morphine tolerance produced by betaarrestin-2-dependent impairment of mu -opioid receptor resensitization [J]. J Neurosci,2011,31(19):7122-7130.
[54] Grecksch G,Bartzsch K,Widera A,et al. Development of tolerance and sensitization to different opioid agonists in rats[J]. Psychopharmacology(Berl),2006,186(2):177-184.
[55] Martini L,Whistler J L. The role of mu opioid receptor desensitization and endocytosis in morphine tolerance and dependence[J]. Curr Opin Neurobiol,2007,17(5):556-564.
[56] Celver J,Xu M,Jin W,et al. Distinct domains of the mu-opioid receptor control uncoupling and internalization[J].Mol Pharmacol,2004,65(3):528-537.
[57] Wang H. A cluster of Ser/Thr residues at the C-terminus of μ-opioid receptor is required for G protein-coupled receptor kinase 2-mediated desensitization[J]. Neuropharmacology,2000,39(3):353-363.
[58] Ueda H,Inoue M,Matsumoto T. Protein kinase C-mediated inhibition of mu-opioid receptor internalization and its involvement in the development of acute tolerance to peripheral mu-agonist analgesia [J]. J Neurosci,2001,21(9):2967-2973.
[59] He L,F(xiàn)ong J,von Zastrow M,et al. Regulation of opioid receptor trafficking and morphine tolerance by receptor oligomerization[J]. Cell,2002,108(2):271-282.